Improved nonporous magnetic supports for immobilized enzymes.

Ni powders coated by deposition of TiO2 or controlled oxidation to NiO develop substantial resistance to corrosion. Chymotrypsin immobilized to these coated Ni supports shows very high stability of activity on storage. Chymotrypsin immobilized by adsorption and glutaraldehyde crosslinking was fairly rapidly eluted under operational conditions in the presence of substrate. If 3-aminopropyltriethoxysilane (APS) was used to produce a covalent linkage, desorption of enzyme still occurred because of relatively unstable bonding of the silane to the oxide surface. A more stable attachment was produced by joining together many silane links with a layer of polyglutaraldehyde. The mechanism of action of APS as a coupling agent under these conditions is discussed. gamma-Fe2O3, and particularly a Mn-Zn ferrite, are suitable magnetic support materials available with smaller particle sizes. Particles below 1 mum give the expected higher specific activities of immobilized enzymes.     

Influence of chloroplast development on the activation of the diphenyl ether herbicide acifluorfen-methyl

The activity of acifluorfen-methyl (AFM); methyl 5-(2-chloro-4-[trifluoromethyl] phenoxy)-2-nitrobenzoate in excised cucumber cotyledons (Cucumis sativus L.) was examined. AFM induced membrane disruption, was significantly greater when etiolated cotyledons were illuminated 16 hours at 150 microeinsteins per square meter per second photosynthetically active radiation versus incubation under illumination of 4-fold greater intensity. These results were unexpected since the loss of membrane integrity is initiated by photodynamic reactions. Untreated, etiolated cotyledons were not able to accumulate chlorophyll under the higher light intensity while control and herbicide treated cotyledons greened significantly under the lower intensity illumination suggesting that some process associated with greening stimulated AFM activity. Inhibition of greening by cycloheximide also reduced AFM activity. Intermittent lighting induced greening in AFM treated cotyledons without causing any detectable loss of plasmalemma integrity. Utilization of this system for pretreatment of cotyledons prior to continuous illumination revealed that activity was greater when tissue was greened in the presence of AFM than when herbicide treatments were made after a greening period of the same duration. The results indicate that the pigments in situ in etiolated tissue are sufficient, without greening, to initiate membrane disruption by AFM. However, greening increases the herbicidal efficacy greatly. Furthermore, the stimulation appears to be due to specific interactions between AFM and the developing plastid and is not attributable solely to an increase in endogenous photosensitizers.     

Biocatalysis in multi-phase reaction mixtures containing organic liquids

A wide range of enzymes and whole microbial cells will act as catalysts in reaction mixtures that contain 2 or more phases, one of which is an organic liquid (either a reactant or including water-immiscible organic solvents). These "biphasic" systems have a variety of structures, knowledge of which aids predictions about biocatalyst activity and stability. There is often a dilute aqueous solution phase (containing the biocatalyst), which may be emulsified with the organic phase, or "trapped" within catalyst particles; sometimes however there may only be traces of water adsorbed to the enzyme or cells. These reaction systems offer several advantages for industrial applications, notably the higher solubilities of many reactants of interest, and the ability of readily available hydrolytic enzymes to catalyse syntheses. The most non-polar organic liquids are least likely to inactivate biocatalysts, though many do remain active with relatively polar solvents. Modification of the biocatalyst may stabilise against inactivation, especially where this is due to direct contact with the phase interface. The mass transfer processes required in these systems remain poorly understood, particularly because the interfacial area is often unknown. Attractive continuous reactors may be operated using a packed bed of catalyst with a trapped aqueous phase.     

New solution method for equations of reaction and mass transfer in biocatalyst particles

Summary For numerical solution of the reaction-mass transfer equations for immobilised biocatalysts it may be better to start integration at the particle surface and proceed inwards: calculations are targetted on the region to which practically interesting changes are often confined (because concentrations are effectively zero in the interior); and during iterative solution wrong initial estimates may be rejected after detecting anomalies early in the integration.Symbols C_b substrate concentration in bulk (mol m^–3) - c dimensionless substrate concentration (C/C_b) (-) - D_e effective diffusion coefficient (m²s^–1) - Da Damkohler number (V.r_o ²/D_e.K_s) (-) - K_s substrate concentration kinetic coefficient (mol m^–3) - k_e external mass transfer coefficient (ms^–1) - r_o bead radius (m) - Sh Sherwood number (k_e.r_o/D_e) (-) - V maximum rate per unit volume in beads (mol m^–3s^–1) - x dimensionless distance from bead centre (r/r_o) (-) - dimensionless kinetic coefficient (K_s/C_b) (-) - _o effectiveness factor (-)     

Rhodocybe pulchrisperma (Entolomataceae): A new species from North America

Rhodocybe pulchrisperma is described as a new species of Agaricales from North America. It belongs in section Rhodocybe due to the brightly colored pseudocystidia and lack of clamp connections. The very large, handsomely ornamented basidiospores distinguish this species from others in the section. A key to taxa from Florida, Papua New Guinea, and India that exhibit similar features is presented.     

Steroid synthesis in ovarian homogenates from immature mice treated with diethylstilboestrol in neonatal life

Female mice of the NMRI strain were treated with the synthetic oestrogen diethylstilboestrol (DES) for the first 5 days after birth. Pools of ovaries were removed from groups of 6-, 12-, 21-, 28- and 56-day-old females. An homogenate of an ovarian pool was incubated for 1 h in the presence of [3H]pregnenolone. Synthesized steroids were extracted and separated in a two-dimensional thin-layer chromatography system. Homogeneity of tentative steroids was verified with recrystallization to constant specific activity. Synthesis of [3H]progesterone and [3H]testosterone was demonstrated at 6 days, [3H]androstenedione at 12 days, [3H]17 alpha-hydroxyprogesterone at 21 days, and [3H]oestradiol-17 beta at 28 days. Up to 28 days (21 days for progesterone), the synthetic activity was lower in homogenates of DES-exposed ovaries than in control homogenates. After 28 days, values for recovered [3H]progesterone, [3H]androstenedione and [3H]oestradiol-17 beta were higher in DES homogenates than in control homogenates while the reverse was true for [3H]17 alpha-hydroxyprogesterone and [3H]testosterone. The results are compatible with an early and direct DES inhibitory effect on ovarian steroidogenesis and, later in immature life, a DES-induced disruption of the normal FSH-LH stimulation of ovarian development.     

Notes on Collybia V. Gymnopus section Levipedes in tropical South America,with comments on Collybia

Five species of Gymnopus section Levipedes are reported for tropical South America. Two of these, Gymnopus macropus and G. nubicola, are newly described. Collybia laccata is considered synonymous with G. mucubajiensis comb. nov. now known from Andean Ecuador; both were originally described from the Venezuelan páramo. Gymnopus alkalivirens and G. semihirtipes are compared to G. mucubajiensis. Gymnopus spongiosus, previously known from the eastern United States, is newly reported from Colombian Quercus forests and is proposed as a new combination. Gymnopus dryophilus is, at present, not known from tropical South America, but extralimital material from nearby Costa Rica is described for comparison. No known species of Collybia s.str. have been identified from tropical South America.